Solutions for use as plasma expanders and substitutes

ABSTRACT

An artificial plasma-like substance having at least one water soluble polysaccharide oncotic agent selected from the group consisting of high molecular weight hydroxyethyl starch, low molecular weight hydroxyethyl starch, dextran 40 and dextran 70, which is buffered by lactate and has a pre-administration pH of between 4 and 6.5 is disclosed. In one embodiment, the artificial plasma-like solution may have at least two water soluble polysaccharide oncotic agents one of which is eliminated from the circulation slowly and the other of which is eliminated from the circulation quickly. Supplementation of the plasma-like solution with certain ions is described. A system for administration of the plasma-like solution to a subject wherein the system comprises a first and second solution each having particular buffers is described. Methods for the administration of the plasma-like solution are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of application Ser.No. 08/896,824 filed Jul. 18, 1997; which application is a continuationof application Ser. No. 08/253,384 filed Jun. 3, 1994 and now issued asU.S. Pat. No. 5,702,880; which application is a continuation-in-part ofapplication Ser. No. 08/133,527 filed Oct. 7, 1993 and now abandoned;which application is a continuation-in-part of application Ser. No.08/071,533 filed Jun. 4, 1993 and now issued as U.S. Pat. No. 5,407,528;the disclosures of which applications are herein incorporated byreference.

INTRODUCTION

[0002] 1. Field of the Invention

[0003] The invention relates to the field of plasma-like solutions whichmay be used to treat hypovolemic subjects or to substitute for the bloodor plasma of a subject.

[0004] 2. Background

[0005] Perfusion solutions and blood substitutes are known. The bloodsubstitutes of Collins et al, Kidney preservation for transplantation.Lancet 1219-1222 (1969); Collins G. M., Hypothermic kidney storage.Transplant. Proc. I:1529 (1977); Filcher et al, Flush solution 2, a newconcept for one to three day hypothermic renal storage preservation.Transplantation 39:2, 122-126 (1985); Robs et al, 72-hour canine kidneypreservation without continuous perfusion. Transplantation 21:498(1976); Sacks et al, Transplantation 19:283 (1974) and Kallerhoff et al,Effects of the preservation conditions and temperature on tissueacidification in canine kidneys. Transplantation 39:5, 485-489 (1985)all consist only of low molecular weight molecules that readily traversethe capillary bed of the subject and thus are generally incapable ofmaintaining proper ionic or fluid balance or plasma volume when used inan intact mammalian subject.

[0006] Klebanoff and Phillips, Cryobiology 6:121-125 (1969) disclosedhypothermic asanguinous perfusion of dogs with 11 of 15 subjectssurviving up to 95 minutes when perfused with buffered Ringer's lactateat 7.1 to 16 degrees C. (44.6-60.4 degrees F.).

[0007] Those blood substitutes that have an impermeable substance tomaintain volume use human serum albumin or a mixture of plasma proteins,as the impermeate molecule to maintain blood volume. These are disclosedin Wall et al., Simple hypothermic preservation for transporting humanlivers long distances for transplantation, Transplantation, 23:210(1977); Belzer et al., Combination perfusion-cold storage for optimumcadaver kidney function and utilization, Transplantation 39:2, 118-121,(1985). Haff et al., Journal of Surgical Research 19:1, 13-19 (1975)describe the asanguineous hypothermic perfusion of dogs using twosolutions: the first, a flush solution comprised of pooled delipidatedhomologous plasma and electrolytes, and the second comprised of pooleddelipidated homologous plasma, electrolytes and additional potassiumchloride at a concentration of 10 milliEquivalents/liter (mEq/l). Haffet al also disclose the use of a pulsatile pump oxygenator andhypothermic perfusion with their solutions and suggest that theprocedures could be used for long distance transport of cadaver organdonors and as an alternative to hypothermic circulatory arrest forblood-free intricate surgery.

[0008] Non plasma-based solutions for organ preservation are disclosedin Bishop et al., Evaluation of hypertonic citrate flushing solution forkidney preservation using the isolated perfused rat kidney.Transplantation 25:5, 235-239 (1978). This article discloses a perfusionsolution that included 50 g/liter dextran 40, a concentration thatdiffers markedly from those of the solutions of the present invention.In addition, the electrolyte and ion concentrations differ markedly fromthose disclosed for the present invention.

[0009] Segall et al., Federation Proceedings 44(3):623, (1985) disclosethat a Ringer's lactate-based heparinized blood substitute containing 6%dextran 40 was used to lower the body temperature of hamsters prior tothe circulation of cold-protective solutions, which are not disclosed,for 1 to 1.5 hours.

[0010] Segall et al., (1987) Federation Proceedings, page 1338, disclosethat a blood substitute, which included dextrose (180 mg/dl) and 25 mMHEPES, was used to perfuse a dog to 3° C. when perfusion was stoppedentirely. There is no disclosure of the complete composition of theblood substitute.

[0011] Segall et al, U.S. Pat. No. 4,923,442 and the reissue thereofdisclose a number of solutions used in blood substitution of livingsubjects all of which include at least some concentration of acardioplegia agent, usually potassium ion. Segall et al., U.S. Pat. No.4,923,442 also discloses surgical methods, particularly in respect toinstrument placement and the control of pulmonary wedge pressuregenerally applicable to perfusion of subjects. U.S. Pat. No. 4,923,442and its reissue are incorporated herein by reference.

[0012] Segall et al., U.S. Pat. No. 5,130,230 discloses a bloodsubstitute which may be used as a system of solutions in which a numberof solutions, in some embodiments two solutions and in other embodimentsfour solutions, are used sequentially to completely replace the blood ofliving subjects. In one of the embodiments, one of the solutions,identified as the recovery solution, of a four solution system isdisclosed as having, in addition to several dissolved salts and otherconstituents, dissolved potassium chloride in a concentration range of 0to 10 mM. In describing the blood substitute, the specification of U.S.Pat. No. 5,130,230 discloses that the blood substitute comprises “anaqueous solution of electrolytes at physiological concentration, amacromolecular oncotic agent, a biological buffer having a bufferingcapacity in the range of physiological pH, simple nutritive sugar orsugars, magnesium ion in a concentration sufficient to substitute forthe flux of calcium across cell membranes. The blood substitute alsoincludes the forgoing solution and a cardioplegia agent such aspotassium ion in a concentration sufficient to prevent or arrest cardiacfibrillation.” Thus potassium ion at physiological concentration is partof the base solution of the disclosed blood substitute. Thespecification also discloses that concentration of cations includingMg⁺⁺, Ca⁺⁺ and K⁺ in excess of that normally found in mammalian bloodare suitable for exerting a cardioplegia effect. Lastly thespecification discloses that the blood substitute may be used as a bloodvolume expander and that “(f)urthermore if the blood substituteaccording to the invention is used as a blood volume expander in asubject at non-hypothermic temperatures, the cardioplegia agentdescribed . . . will generally be omitted so that normal cardiacfunction can be maintained.” From the forgoing it is clear that theblood substitute when used as a blood volume expander at normal bodytemperatures contains K⁺ at physiological concentrations but not inconcentrations sufficient to cause cardioplegia.

[0013] Commercial products used for the treatment of hypovolemicpatients are known and include Hespan (6% hetastarch 0.9% Sodiumchloride Injection [Dupont Pharmaceuticals, Wilmington Del.]), Pentaspan(10% pentastarch in 0.9% Sodium chloride Injection [DupontPharmaceuticals, Wilmington Del.]) and Macrodex (6% Dextran 70 in 5%Dextrose Injection or 6% Dextran 70 in 0.9% Sodium chloride Injection[Pharmacia, Inc. Piscataway, N.J.]) and Rheomacrodex (10% Dextran 40 in5% Dextrose Injection or 10% Dextran 40 in 0.9% Sodium chlorideInjection [Pharmacia, Inc. Piscataway, N.J.]). These products are knownto the medical community for particular FDA approved indications and areextensively described in the volume entitled Physicians' Desk Reference,published annually by Medical Economics Company Inc.

[0014] Water-soluble and aqueous colloid preparations of vitamin K areknown and are sold respectively under generic names menadiol sodiumdiphosphate (tradename SYNKAVITE®) and phytonadione MSD, USP (tradenameAquaMEPHYTON®) by Roche Labs and Merck Sharp & Dohme, respectively.

SUMMARY AND OBJECTS OF THE INVENTION

[0015] It is an object of the invention to provide a blood plasmaexpander comprising a water soluble polysaccharide oncotic agentsupplemented with calcium chloride at physiological concentration.

[0016] It is a further object of the invention to provide a blood plasmaexpander comprising a water soluble polysaccharide oncotic agentsupplemented with sodium chloride at physiological concentration andmagnesium ion at sub-physiological concentration.

[0017] It is a yet further object of the invention to provide a bloodplasma expander comprising a water soluble polysaccharide oncotic agentsupplemented with sodium chloride at physiological concentration andmagnesium ion at sub-physiological concentration and potassium ion atsub-physiological concentration.

[0018] Another object of the invention to provide a blood plasmaexpander comprising at least two water soluble polysaccharide oncoticagents one of which is eliminated from the circulation slowly and theother of which is eliminated from the circulation quickly.

[0019] Yet another object of the invention is to provide a bufferedblood plasma substitute comprising a water soluble polysaccharideoncotic agent.

[0020] A yet further object of the invention is to provide a bloodplasma substitute comprising a water soluble polysaccharide oncoticagent buffered by lactate and supplemented with sodium chloride atphysiological concentration.

[0021] Still another object of the invention is to provide a bloodplasma substitute comprising a water soluble polysaccharide oncoticagent buffered by lactate and sodium bicarbonate and supplemented withsodium chloride at physiological concentration.

[0022] Still yet another object of the invention to provide a bloodplasma substitute comprising at least two water soluble polysaccharideoncotic agents one of which is eliminated from the circulation slowlyand the other of which is eliminated from the circulation quickly,wherein the blood plasma substitute is buffered and supplemented withsodium chloride at physiological concentration.

[0023] It is yet another object of the invention to provide a method forexpanding the blood volume of a subject in need thereof by administeringintravenously to such subject a blood plasma expander comprising a watersoluble polysaccharide oncotic agent supplemented with sodium chlorideand calcium chloride at physiological concentration.

[0024] Still a further object of the invention is to provide a methodfor expanding the blood volume of a subject in need thereof byadministering intravenously to such subject a blood plasma expandercomprising at least two water soluble polysaccharide oncotic agents oneof which is eliminated from the circulation slowly and the other ofwhich is eliminated from the circulation quickly.

[0025] Yet another object of the invention is to provide a method ofsubstituting the blood plasma of a subject in need thereof byadministering intravenously to such subject a blood plasma substitutecomprising a water soluble polysaccharide oncotic agent buffered bylactate and supplemented with sodium chloride at physiologicalconcentration.

[0026] Still yet another object of the invention is to provide a methodof substituting the blood plasma of a subject in need thereof byadministering intravenously to such subject a blood plasma substitutecomprising a water soluble polysaccharide oncotic agent buffered bylactate and sodium bicarbonate and supplemented with sodium chloride atphysiological concentration.

[0027] Yet still another object of the invention is to provide a methodof substituting the blood plasma of a subject in need thereof byadministering intravenously to such subject a blood plasma substitutecomprising at least two water soluble polysaccharide oncotic agents oneof which is eliminated from the circulation slowly and the other ofwhich is eliminated from the circulation quickly buffered by lactate andoptionally with sodium bicarbonate and supplemented with sodium chlorideat physiological concentration.

DESCRIPTION OF THE INVENTION

[0028] The present invention comprises a mixture of components includingat least one water soluble polysaccharide oncotic agent and preferably amixture of two or more water soluble polysaccharide oncotic agentswherein one is capable of relatively quick elimination from thecirculation and the other is capable of relatively slow elimination fromthe circulation. The mixture also generally includes sufficient sodiumchloride to yield a physiologic concentration approximating that ofhuman serum and sufficient calcium ion to yield a concentration in arange of 80 to 110 milligrams per liter.

[0029] In addition as an aqueous solution the forgoing mixture may alsoinclude magnesium ion in a concentration range which is less than 1 mEqand at least 0.5 mEq/l. Furthermore, optionally the forgoing mixture mayinclude potassium ion at a concentration range of about 2 to 3 mEq/l.Both of the forgoing concentration ranges of magnesium ion and potassiumion are considered to be sub-physiologic for primates and especiallyhuman beings.

[0030] In greater detail, the present invention comprises a mixture ofcomponents which when placed in aqueous solution may be used to expandthe plasma volume of a subject in need thereof. The forgoing componentsmay be provided as a dry sterile mixture to which sterile diluent suchas water, saline solution or dextrose solution may be added to form anaqueous solution. If provided as a dry sterile mixture, the materialsmay be provided in a sterile container suitable for mixture with sterilediluent such as sterile water, sterile saline or sterile dextrosesolution. Alternatively the mixture of materials may be provided in asterile container as an aqueous solution.

[0031] If the mixture of components according to the invention isprovided as a dry sterile mixture suitable for fluid addition by asterile saline solution, the amount of chloride salt of sodium in thedry mix is adjusted or omitted in amount equal to the sodium chloridecontained in the sterile saline solution used. If the mixture accordingto the invention is provided as an aqueous solution, it is preferable toprovide the solution as a sterile solution in a sterile container.Alternatively, the aqueous solution according to the invention may beprovided as a non-sterile solution and may be subsequently sterilefiltered into or autoclaved in sterile containers.

[0032] In another embodiment of the invention, the solution may beprovided as a small volume sterile aqueous solution containing themixture of components according to the invention in high concentration,which when mixed with a predetermined volume of an existing commerciallyavailable sterile oncotic solutions such as a commercial preparation ofhigh molecular weight hydroxyethyl starch sold under the trade nameHespan (DuPont) or low molecular weight hydroxyethyl starch sold underthe trade name Pentaspan (DuPont) provides a solution with the buffer orbuffers and ions in the concentrations described herein in accordancewith the invention.

[0033] For purposes of the further description of the invention, themixture of components according to the invention will be discussed as anaqueous solution. From the following description of the invention it isexpected that one ordinarily skilled in the art would be enabled toprovide the mixture as a dry mixture and make the adjustments to amountsof sodium chloride and or dextrose as necessary to accommodate theamounts of sodium chloride found in normal saline solution for injectionof a dextrose solution for injection, which may be used as a diluent forthe dry mixture according to the invention.

[0034] The polysaccharide oncotic agents of the forgoing mixture ofcomponents are ones that are water soluble. By water soluble is meantthat the polysaccharide will dissolve in water readily or with stirringor shaking. By water soluble oncotic agent is meant water solublemolecules which whendissolved in the fluid phase of circulating plasmain a living subject are of a size sufficient to prevent their immediateloss from the circulation by traversing the fenestration of thecapillary bed into the interstitial spaces of the tissues of the body.The term polysaccharide oncotic agent thus does not include suchpolysaccharides as chitin since chitin is not soluble in water.

[0035] Polysaccharides that are water soluble and can act as oncoticagents are generally characterized as glucan polymers. In general, it ispreferred that the water soluble polysaccharide oncotic agent is aglucan polymer that is non-antigenic.

[0036] Hetastarch which is a tradename for hydroxyethyl starch is aglucan polymer which can act as an artificial colloid when dissolved inwater. Hydroxyethyl starch is derived from a waxy starch composed almostentirely of amylopectin with hydroxyethyl ether groups introduced intoglucose units of the starch and the resultant material is hydrolysed toyield a product with a suitable molecular weight. The molar substitutionof the hydroxyethyl moiety is 0.7 which means hydroxyethyl starch has 7hydroxyethyl groups for every 10 glucose units. The average molecularweight of hydroxyethyl starch is 480,000 with a range of 400,000 to550,000. and with 80% of the polymers falling in the range of 30,000 to2,400,000. Hydroxyethyl groups are attached by ether linkage primarilyat C2 of the glucose unit and to a lesser extent the C3 and C6 position.The glucose units are joined primarily in alpha (1-4) linkage withoccasional 1-6 branches. The colloid properties of a 6% solution (wt/wt)of Hydroxyethyl starch approximates that of human serum albumin, withapproximately 33% of a 500 ml intravenous dose eliminated in the urineafter 24 hours. Approximately 10% of the dose remains circulating after1 week. As used herein Hydroxyethyl starch is referred to as highmolecular weight hydroxyethyl starch.

[0037] Pentastarch is another glucan polymer which can act as anartificial colloid when dissolved in water. Pentastarch is also derivedfrom a waxy starch composed almost entirely of amylopectin withhydroxyethyl ether groups introduced into glucose units of the starchand the resultant material is hydrolysed to yield a product with asuitable molecular weight. The molar substitution of the hydroxyethylmoiety is 0.45 which means pentastarch has 45 hydroxyethyl groups forevery 100 glucose units. The average molecular weight of pentastarch isapproximately 264,000 with a range of 150,000 to 350,000 and with 80% ofthe polymers falling in the range of 10,000 to 2,000,000. Hydroxyethylgroups are attached by ether linkage primarily at C2 of the glucose unitand to a lesser extent the C3 and C6 position. The glucose units arejoined primarily in alpha (1-4) linkage with occasional 1-6 branches. Asused herein pentastarch is referred to as low molecular weighthydroxyethyl starch.

[0038] Other polysaccharide derivatives may be suitable as oncoticagents in the solutions according to the invention includinghydroxymethyl alpha substituted (1-4) or (1-6) polymers. Cyclodextrinssuch as hydroxypropyl substituted β or γ cyclodextrin may be suitable asoncotic agents in the blood substitute according to the invention.

[0039] D-glucose polymers that are soluble in water may also be used asthe water polysaccharide oncotic agent in the mixture according to theinvention. Examples of such D-glucose polymers are Dextran, which isD-glucose linked predominantly in alpha (1-6) linkage, Dextran in amolecular weight range of 30,000 to 50,000 daltons (D) are preferred.Most preferred is Dextran 40 having a molecular weight of about 40,000D.

[0040] The concentration of the polysaccharide oncotic agent in thesolution according to the invention will be sufficient so that asignificant amount of the oncotic agent is still circulating in asubject 2 to 5 days after administration of the solution. Accordingly,the solution according to the invention will have a mixture of highmolecular weight and low molecular weight poly-saccharide oncotic agentsthe relative amounts of which have been optimized to achieve this effectin this time period. The solution according to the invention willpreferably contain a lower or equal concentration of higher molecularweight polysaccharide oncotic agents as compared to the concentration oflower molecular weight polysaccharide oncotic agents. Higher molecularweight polysaccharide oncotic agents such as high molecular weighthydroxyethyl starch and dextran 70 are generally eliminated from thecirculation at a slower rate than lower molecular weight polysaccharideoncotic agents such as low molecular weight hydroxyethyl starch anddextran 40. High molecular weight hydroxyethyl starch is eliminated fromthe circulation of a human being slowly. Approximately 33% of a 500 mlinfusion of 6% high molecular weight hydroxyethyl starch is eliminatedfrom the circulation after 24 hours, with approximately 10% of the doseremaining in the circulation after 2 weeks. Low molecular weighthydroxyethyl starch is eliminated from the circulation of a human beingquickly. Approximately 70% of a 500 ml infusion of 10% low molecularweight hydroxyethyl starch is eliminated from the circulation after 24hours, with approximately 20% of the dose remaining in the circulationafter 1 week. Elimination time for 6% dextran 40 and similar lowmolecular weight water soluble polysaccharide oncotic agents aresimilar.

[0041] When Dextran 40 or low molecular weight hydroxyethyl starch isused in the solution according to the invention its concentration is ina range of 6.0 to 8.5%. A solution comprising about 8% Dextran 40(wt/wt) or about 80 grams (g) per liter (l) of water is generally used.When Dextran 70 or high molecular weight hydroxyethyl starch is used inthe solution according to the invention its concentration is in a rangeof 5.5% to 6.5%. A solution comprising about 6% high molecular weighthydroxyethyl starch (wt/wt) or about 60 grams (g) per liter (l) of wateris generally used.

[0042] When it is necessary to treat a subject who has lost asignificant amount of blood, generally up to about 30% to 40% of bloodvolume with a plasma expander, the forgoing mixture may be administeredintravenously as a sterile aqueous solution. In another embodiment ofthe invention, the oncotic agent is a mixture of high molecular weightwater soluble polysaccharide, such as high molecular weight hydroxyethylstarch or dextran 70, and low molecular weight water solublepolysaccharide, such as low molecular weight hydroxyethyl starch ordextran 40. In this embodiment of the invention which may beparticularly useful when it is not possible to transfuse a subject withwhole blood quickly, the amount of high and low molecular weighthydroxyethyl starch is adjusted to initially stabilize the colloidosmotic pressure of the subject's blood and then to gradually remove thewater soluble oncotic agent as the patient begins to replenishcirculating serum proteins.

[0043] Solutions according to the invention having this composition willtypically include high molecular weight hydroxyethyl starch in a rangeof from 5 to 40 grams per liter and dextran 40 or low molecular weighthydroxyethyl starch in a concentration of 20 to 75 grams per liter;however the concentration of the two water soluble oncotic agentstogether will generally not exceed 80 grams per liter. It is believedthat a solution comprising about 20 grams per liter high molecularweight hydroxyethyl starch and about 50 grams per liter of dextran 40 orabout 50 grams per liter of low molecular weigh hydroxyethyl starch isdesirable. A solution comprised of about 30 grams per liter highmolecular weight hydroxyethyl starch and about 30 grams per liter ofdextran 40 or about 30 grams per liter of low molecular weighthydroxyethyl starch may be preferred.

[0044] In determining the amount of the two oncotic agents in thesolution according to the invention, the amounts of the two agents areadjusted to maintain oncotic balance without infusing so much of theoncotic agent that the plasma becomes hyperoncotic and circulating serumproteins are removed from the circulation by hepatic absorption or renalexcretion or other physiological mechanisms. Thus it is important thatthe high molecular weight hydroxyethyl starch or dextran 70 and lowmolecular weight hydroxyethyl starch or dextran 40 should not togetherexceed about 8% weight/volume percent. Solutions exceeding thisconcentration of oncotic agent may be physiologically hyperoncoticleading either to removal of serum protein from the circulation or aninhibition of their production. Since high molecular weight hydroxyethylstarch and dextran 70 are not quickly eliminated from the circulationthe amount of these oncotic agents will generally not be more than 75%of the total weight of the water soluble oncotic agents in the solution.By using a high molecular weight oncotic agent in the solution incombination with a low molecular weight solution, the addition of thesolution to a subject's circulation either as a plasma expander aftertrauma or surgery, or as a blood substitute when more than 30% of thesubject's circulating volume is made up of the blood substitute, thesubject's circulating oncotic pressure is quickly stabilized, fluidexchange between the circulating blood compartment and the interstitialspaces is minimized, and edema is curtailed. Furthermore, the rate ofelimination of the low molecular weight oncotic agent is sufficientlyquick that oncotic balance can be maintained without inhibiting thesubject's production of new serum proteins, while at the same time therate of elimination of the high molecular weight oncotic agent issufficiently slow that the polysaccharide oncotic agent is able tomaintain oncotic balance until sufficient protein has been producedafter substantially complete elimination of the low molecular weightpolysaccharide oncotic agent.

[0045] The solutions according to the invention with calcium andmagnesium ions provided by the solution have the advantage of providingessential ions required for the patient's blood to maintain its abilityto clot. This advantage may be significant to a patient suffering from ahemorrhage or internal bleeding with concomitant loss of blood pressuredue to decreased blood volume. In these patients the administration ofconventional plasma expanders such as Hespan, Pentaspan, Macrodex andRheomacrodex may lead to dilution of blood plasma proteins and ionsessential to the formation of blood clots which may be life savingparticularly for trauma patients. If the conventional plasma expandersare used, dilution of the blood proteins and electrolytes essential forclotting may have fatal consequences. By administering the solutionaccording to the invention, the provision of essential electrolytes willlead to a greater preservation of the ability of the patient's blood toclot if necessary.

[0046] In the solution according to the invention the magnesium ionconcentration will range between 0.5 and 0.9 mEq/l. Magnesium ion isgenerally sequestered intracellularly in an intact mammalian subject;however in the event of trauma which damages tissues, magnesium ionconcentration will increase. Thus it is desirable to administer thesolution according to the invention with magnesium ion concentrations onthe low end of this range when tissue damage has occurred. Typicallythis will be in situations wherein the solution is administered tomaintain the blood volume of a trauma victim. By contrast, when thesolution is used to substitute for the blood of a subject, such as whensurgical procedures at low temperature are carried out, it is desirableto administer the solution according to the invention with magnesium ionconcentrations at the high end of the range. In either case theconcentration of the electrolyte. magnesium ion is one that is generallyconsidered to be less than physiological. When a subject's bloodmagnesium ion concentration falls below normal several problems mayoccur including tetany and irregular heartbeat. In maintainingelectrolyte levels in normal human subjects, magnesium ion concentrationof less than 0.5 mEq/l are considered to be “panic levels”ie.-concentrations which require immediate intervention andadministration of available high concentration magnesium ion containingsolutions to normalize the magnesium ion concentration. The normalphysiological range for magnesium ion in blood is generally consideredto be 1-2 mEq/l. Thus the solutions according to the inventionunexpectedly use magnesium ion concentrations that are less thanphysiological to maintain subject blood volume or blood substitution atlow temperature. This is unlike the teaching of prior teachings such asU.S. Pat. Nos. 4,923,442 and 5,130,230 and standard nursing texts onmaintenance of proper electrolyte balance.

[0047] It has been discovered that the utility of the forgoing solutionswhich may be used as plasma volume expanders, may be extended by alsoincluding a sufficient amount of a water soluble preparation or aqueouscolloid suspension of vitamin K to stimulate the liver to produce bloodserum proteins essential to maintaining normal blood clotting function,usually expressed as the time it takes for a standard volume of wholeblood or blood plasma to clot. In general, a concentration of vitamin Kin the solution sufficient to deliver about 5 to 10 mg of vitamin K tothe subject is required in the solution according to the invention. Thusif 2-3 liters of solution are delivered to the patient's circulation aconcentration of 2 to 3 mg of vitamin K per liter will be used. It isbelieved that a concentration of about 2.5 mg vitamin K is optimal forthis purpose.

[0048] The foregoing solutions may also be augmented, optionally, by asmall amount of potassium ion generally in a concentration range between2 to 3 mEq/l. The use of potassium ion in this concentration range maybe indicated in individuals who have lost a substantial amount of bloodbut who have not been subject to extensive tissue trauma or whole bloodtransfusion. In both of these latter conditions, significant amounts ofpotassium ion may be released into the blood stream by lysis of bloodcells or tissue cells. If high concentrations of potassium ion releasedby such trauma or transfusion prevail in the blood for a significantperiod of time, particularly as a result of lowered renal perfusion andfiltration rates because of low blood volume, it may be desirable toomit potassium ion from the solution administered to such patients. Onthe other hand if normal potassium concentrations are present in thesubject's remaining circulating blood, it will be desirable to includepotassium in the solution according to the invention.

[0049] One of the problems in treatment of hypovolemic patients who havelost substantial amounts of blood, generally greater than 30% of theirnormal blood volume, is the need to provide in addition to essentialelectrolytes, and reasonable oncotic balance, sufficient ability tomaintain pH and nutrition of the central nervous system, while at thesame time permitting the remaining blood in the subject to functionnormally. Patients who have lost 30% or greater of their blood volumeand who are treated with Hespan® frequently experience breaking of theirred blood cells or hemolysis in addition to other problems associatedwith extreme hemodilution such as reduced clotting time and prothrombinlevels.

[0050] In individuals who have lost more than 30% of their blood it isdesirable to further augment the forgoing solutions as described furtherherein below with respect to buffering capacity to maintain proper pH,assimilable sugar and, particularly when it is difficult to find amatching blood donor or whole blood transfusion would be otherwisedifficult, a material which stimulates the formation of blood proteinsnecessary for proper blood clotting. In particular Vitamin K in a formwhich may be administered in aqueous solution is included at aconcentration effective to stimulate hepatic synthesis of bloodcoagulation factors including prothrombin (factor II) proconvertin(factor VII), thromboplastin (factor I) and Stuart factor (factor X).

[0051] To provide buffering capacity the forgoing solution will includea sufficient amount of buffer to permit effective buffering of thecirculating blood in a pH range around 7.4. In some uses, the buffer issodium lactate at a concentration in a range of 10 to 30 mM, preferablyabout 28 mM. Sodium lactate is preferred because lactate is a compoundnaturally occurring in the body. Additionally, other suitable buffersusable in lieu of lactate are small organic acid ions that may bemetabolized such as acetate, pyruvate, gluconate and succinate. Citrateshould not be used since it adversely affects the ability of whole bloodto clot. NaHCO₃ (sodium bicarbonate) will be provided as a bufferinaddition to sodium lactate, in a concentration of about 5 to 10milliMolar (mM). It is also possible to use a biological buffer such asHEPES or a balanced solution of Trizma base and Trizma HCl in lieu oflactate or bicarbonate. When Trisma base/Trizma HCl is used to providebuffering, these components are added in the amount of about 0.83 and2.86 grams per liter of solution respectively; however biologicalbuffers are preferably not used unless the oncotic agent is provided bya mixture of water soluble high and low molecular weightpolysaccharides.

[0052] Vitamin K which is compatible with aqueous media for injectionwill be preferred in the solution according to the invention.Preparations of this general type are known and are sold aspharmaceutical preparations in their own right under various names suchas menadiol sodium diphosphate, which is a synthetic water-solublederivative of menadione vitamin K3 (Roche, Nutley N.J.) and phytonadionewhich is a clear aqueous dispersion of vitamin K.sub.1 (Merck Sharp &Dohme). In general the concentration of aqueous vitamin K in thesolution according to the invention will be sufficient to deliverbetween 5 to 10 milligrams to the subject. The wide range of vitamin Kconcentration is necessary to accommodate patients in age and weightfrom infant to adult.

[0053] The solution according to the invention for administration topatients who have lost more than 30% of their blood volume will alsoinclude an easily assimilable sugar. In general dextrose (glucose) ispreferred in a concentration sufficient to sustain nutritionparenterally. In general a concentration of about 5 mM glucose will beused.

[0054] When used as a blood plasma expander in a hypovolemic subject,the solution according to the invention will be administered in anamount up to about 30% of the average blood volume of an averagesubject. If the subject is the size of an average adult male human beingthe average blood volume is about 5000 ml and the volume of the solutionaccording to the invention will be up to about 1500 ml. The compositionof the solution according to the invention used as a blood plasmaexpander will generally comprise an aqueous solution of water solublepolysaccharide oncotic agent, with dissolved Sodium chloride atphysiologic concentration (about 0.9% or 154 mM), calcium chloride at aconcentration of about 2.5 mM and optionally magnesium chloride in aconcentration range which is less than 1 mEq/l and at least 0.5 mEq/l Ingeneral a magnesium chloride concentration of about 0.475 mM ispreferred. The water soluble polysaccharide may be high molecular weighthydroxyethyl starch dextran 70 or dextran 40 in a concentration of about60 grams/liter. Optionally, the forgoing mixture may include potassiumion at a concentration range of about 2 to 3 mEq/l. In an additionaloption the solution may also include aqueous vitamin K in aconcentration sufficient to deliver between 5 to 10 milligrams to thesubject. When administered to a subject the solution according to theinvention will be administered intravenously as a sterile solution by acontinuous fast infusion.

[0055] When used as a blood replacement in a severely hypovolemicsubject or when used in a procedure in which the subject blood isdeliberately removed, the solution will be administered as a sterilesolution in an amount exceeding 30% of the average blood volume and willgenerally exceed 1500 ml. The composition of the solution according tothe invention used as a blood replacement will generally comprise thecomponents in the amounts described in the preceding paragraph. Ifadministered to a mammalian subject that has been chilled to hypothermicbody temperatures, (generally 5 or more degrees Centigrade below normalbody temperature) potassium ion may be completely omitted from thesolution or may be present in sub-physiological amounts up to about 3mEq/l according to the invention. If the solution is administered to asubject that is at normal body temperature, the solution according tothe invention may include potassium ion at a concentration range ofabout 2 to 3 mEq/l.

[0056] In addition, whether administered as a blood replacement to ahypothermic subject or a subject at normal temperature, the solutionwill also contain a buffer. A preferred buffer is lactate at aconcentration of about 28 mM. Sodium lactate is preferred becauselactate is a compound naturally occurring in the body. Alternatively,the buffer will also include a sufficient amount of NaHCO₃ to permiteffective buffering of the circulating blood in a pH range around 7.4.In general, NaHCO₃ will be provided in a concentration of about 5 to 10milliMolar (mM), and preferably at about 5 mM particularly if thesubject's body temperature is 5 degrees Centigrade below normal when thesolution is administered as a blood plasma substitute or blood plasmaexpander.

[0057] Prior art blood substitute solutions generally teach that it isdesirable to provide a buffer that is a biological buffer in a solutionhaving, prior to administration to a subject, a pH range of about 7.2 to7.8. Such buffers are exemplified by HEPES, MOPS, TRIS, and othersimilar buffering salts. Such biological buffers are very expensive, incontrast to the cost of the components in the solutions according to theinvention. The buffering capacity of these biological buffers isgreatest in the pH range 7.2 to 7.8 which is the pH range in whichmammalian subjects normally regulate blood-pH. One great disadvantage ofthese biological buffers is that, although they buffer best at normalphysiological pH in vitro, most are as yet not generally regarded assafe for human administration and none has been used clinically as anintegrated component in a large volume parenteral solution. By contrast,it has been surprisingly found by the inventors that small organic acidsalts such as sodium lactate and sodium bicarbonate can be used asbuffers in the plasma extender and blood plasma substitute solutionsaccording to the invention even though the pH of these solutions priorto administration are not physiological. In the case of lactate alone,the average pH is about 5.5 prior to administration. In the case ofbicarbonate as buffer, the solutions according to the invention have apH greater than pH 8 at room temperature prior to administration.

[0058] The use of these small organic acid salts as buffering agents inthe solutions according to the invention is particularly advantageouswhen the solution is used to substitute a significant amount of asubject's missing blood volume. Thus the use of small organic acid saltsas buffers in the solutions of the invention is particularlyadvantageous when the solution is used to replace or substitute forblood volumes in excess of 30% of the subjects normal circulating bloodvolume. By using small organic acid salts as buffers, such as sodiumlactate or sodium bicarbonate, it is possible to perfuse a subject formany hours using the solutions according to the invention withoutencountering the hazard of uptake and sequestration of chemicalcompounds such as HEPES, MOPS, TRIS and other similar buffering saltsused in prior art solutions such as those disclosed in Segall et al.,U.S. Pat. Nos. 4,923,442 and 5,130,230. Unexpectedly, it has been foundthat despite an initial pre-administration pH of about 5.5, thesolutions according to the invention in both primate and rodent modelsare able to maintain pH of the blood after infusion of 7.2 to 7.8 evenwhen used to substantially and completely replace all of the circulatingblood of a subject.

[0059] In a further embodiment of the invention, Applicants havediscovered that the small molecule organic acid salt is preferablysodium lactate in a concentration sufficient to maintain the solution ata pH of about 5.5 prior to administration, provided that the volume ofblood to be replaced is no greater than about 30% of the blood volumeand is administered at normal mammalian body temperatures. It is alsopreferred to supplement the lactate as buffer in the solution withsodium bicarbonate when the solution is used to substitute more than 30percent of the subject's blood volume, particularly if this substitutionis carried out under conditions wherein the subject is maintained attemperatures between 7 degrees centigrade below normal temperature andabout 1 degree centigrade.

[0060] This discovery is particularly important when one is using thesolution to maintain a subject during procedures in which the subject iscooled to core body temperatures at which the subject is not itselfcapable of maintaining normal physiological homeostatic mechanisms suchas those which maintain blood pH between 7.5 and 7.8. Lactate infusedinitially in the solution according to the invention, does not havesufficient buffering capacity at low temperature. Therefore, in usingthe solution according to the invention to substitute the blood of asubject under cold hypothermic conditions, it is advantageous to use thesolution containing sodium lactate to initially substitute for thesubject's blood, and as the subject's blood is replaced to beginsubstitution using sodium bicarbonate in addition to sodium lactatesince sodium bicarbonate has a greater buffering capacity. Thus,complete substitution may be accomplished using a system of twosolutions, the initial solution comprising sodium lactate as buffer andthe subsequent solution using sodium bicarbonate and sodium lactate.

[0061] When used as a plasma extender, which in general is in situationswhere 30% or less of the subject's normal blood volume is being added(usually after blood loss due to trauma or surgery), the solutionaccording to the invention will usually be administered to a subject atnormal body temperature for that mammalian subject. It is preferred thatthe solution according to the invention, when used as a plasma extenderand administered at about normal body temperature, have only lactate asa buffer, which is provided in the solution as sodium lactate. At normalbody temperatures, lactate may be eventually metabolized by the subjectleaving assimilable (or easily excreted) sodium ion.

[0062] When used as a plasma substitute, which in general is insituations where more than 30% of the subject's normal blood volume isbeing perfused into the subject, usually when the subject's blood isbeing removed at the same time as the solution according to theinvention is administered, the solution according to the invention willusually be administered to a subject that has been chilled to a bodytemperature below normal, usually 7° C. or more below the normaltemperature for that mammalian subject. It is preferred that thesolution according to the invention, when used as a plasma substituteand administered at such sub-normal body temperatures, have in additionto lactate as a buffer, sodium bicarbonate (NaHCO₃). In practice, if theprocess of replacing the subject's blood is started before the subject'sbody temperature is substantially below normal, the solution accordingto the invention with only sodium lactate as buffer will beadministered. As body temperature falls below normal the solutionaccording to the invention with sodium lactate and sodium bicarbonatewill be administered to the subject. Furthermore, during the period oftime that the subject is maintained at below normal temperature, it willbe periodically perfused with fresh solution according to the inventioncontaining both sodium lactate and sodium bicarbonate as buffer. Thesolution according to the invention containing both sodium lactatebuffer and sodium bicarbonate solution is preferred when the subject isto be used for the purpose of harvesting body organs for eventualtransplant and organ preservation is of paramount importance. Inaddition this same solution may be used to perform surgery on a subjectwhen it is necessary to reduce the subject's temperature to slowmetabolic activity and the removal of blood is required to optimize thecondition of the surgical field.

[0063] In one embodiment of the invention 0.9% saline, Ringer's lactate,Plasmalyte, Normasol or other commonly used crystalloid solution can beused to replace up to 50% of the subject's blood instead of thelactate-buffered solution. This solution is then rapidly replaced by thelactate and bicarbonate buffered form of the invention.

[0064] The solutions according to the invention containing lactate havean initial pH prior to administration to a subject of about 4 to 5.5. Itis possible to more easily terminally heat sterilize the solutionsaccording to the invention at pH 5.5, without adversely affecting thestatus of the polysaccharide oncotic agents which tend to caramelizewhen terminally sterilized at pH exceeding 7.0. Sodium bicarbonate maylimit the ability of the solution to be terminally heat sterilized. Tofacilitate use of the solutions according to the invention the solutionmay be supplied as a kit including a terminally heat sterilized solutionincluding all the components of the solution according to the inventionin a ready to use container except sodium bicarbonate and a secondsterile container of pre-measured sterile sodium bicarbonate solutionwhich may be added using sterile technique to the ready to use solution.

[0065] Less preferred buffer in the solutions according to the inventionis a biological buffer such as Hepes or a balanced solution of Trizmabase and Trizma HCl in lieu of Bicarbonate. When Trizma base/Trizma HClis used to provide buffering, these components are added in the amountof about 0.83 and 2.86 grams per liter of solution respectively and arepreferably used only when the water soluble polysaccharide oncotic agentis a combination of high molecular weight and low molecular weightpolysaccharides.

[0066] Also included in the solution according to the invention whenadministered as a blood replacement, the solution will include anassimilable sugar, preferably dextrose at a concentration of about 5 mM.When administered as a blood replacement, the solution may be quicklyinfused through a venous cannula or other indwelling device able topermit large volume infusion. The blood pressure of the subject may bemonitored so that central venous pressure remains below 10 millimetersof mercury. If pressure begins to increase, a volume of blood may beremoved through the venous cannula and the pressure equilibrated at anacceptable level. If desired the solution according to the invention maybe perfused into the subject by means of a pump and closed circuitincluding a reservoir of the solution according to the invention untilthe subject's blood is partially or fully replaced with the solutionaccording to the invention as desired.

[0067] The invention will be better understood in connection with thefollowing examples which are intended by the inventors to beillustrative of the invention but not limiting.

EXPERIMENTAL EXAMPLE I Reviving An Ice-Cold Blood-Substituted BaboonAfter Chilling to Near-Freezing

[0068] A 7 kg male baboon of the species Papio anubias was chilled andblood-substituted to a minimum deep esophageal temperature of 2° C.After reaching that temperature, the animal was warmed, revived andrecovered.

[0069] The baboon was injected i.m. with ketamine. A catheter wasinserted in the right cephalic vein, and 2.5% pentothal injected i.v.The primate was then fitted with an endotracheal tube and placed onflether anesthetic. The animal was shaved, and a Ringer's lactate dripinitiated i.v., with its rate titrated to the animal's arterial bloodpressure. The right femoral artery was catheterized to allow for bloodpressure monitoring, and a 3-way stopcock placed in-line to allowarterial blood sampling every 10-60 minutes throughout the entireprocedure. A wedge catheter was implanted in the pulmonary arterythrough the right radial vein.

[0070] The extracorporeal circuit was constructed with a hard shellvenous reservoir, Biomedicus pump head, hollow fiber membrane oxygenatorwith integral heat exchanger, flow meter and a secondary in-line heatexchanger added as close to the animal as possible. The circuitincorporates a section between the outflow cannula and the venousreservoir to remove effluent and a 1 L funnel/reservoir to quicklyrefill the venous reservoir with blood substitute or blood. A cooler tosupply the oxygenator's built-in heat exchanger and the secondary heatexchanger with circulating ice water (and warm water) was required. Alltubing in contact with blood or blood substitute was sterile. The venousreservoir and circuit was filled with 2 liters of HL solution.

[0071] A catheter was placed in the left brachial vein to allowmonitoring of central venous pressure (CVP). Arterial blood gases, pH,K⁺ and hematocrit are measured in each sample, and in some cases,electrolytes, and enzymes as well.

[0072] Venous outflow cannulas were placed in the left femoral vein. Anarterial inflow cannula was placed in the left femoral artery. After thevenous cannula was implanted, heparin was injected iv. SoluMedrol (12mg/kg) was then injected iv and the eyes coated with a protectiveointment. An esophageal tube was inserted, and Maalox administered. Theesophageal tube was fitted with a temperature probe for recording deepesophageal temperature. The EKG leads are put in place and the animalwas immersed in crushed ice.

[0073] Following the onset of cooling, the animal was managedanesthetically light with 2.5% pentothal (at doses between 1-3 cc). Whenbody temperature reaches 30° C., 200 ml of the solution indicated belowdesignated HL was infused in the brachial vein and an equal amount ofblood was drained from the arterial cannula and collected sterile forlater use. When body temperature dropped below 29° C., anesthetic wasdiscontinued. After chilling to 25° C., the animal was placed on bypass.At that time, the clamps are released which isolate the baboon'scirculation from the bypass circuit, and an amount of HL solutionsufficient to flush substantially all of the animals blood (for the 7 kgbaboon approximately 2 liters of solution) was allowed toblood-substitute the animal, and whole and diluted blood was removed asvenous effluent and saved for revival. Following this, its heart wasarrested by the intra-arterial administration of 2M KCl added via thesecondary heat exchanger.

[0074] After the heart was arrested, the solution indicated belowdesignated HLB was added to the reservoir and circulated into theanimal. As this solution perfused into the animal, a blood-bloodplasma-substitute mixture was continuously removed as a venous effluentuntil the HLB solution replaced the initial circulating solution. Thetemperature was then dropped to 2° C. as rapidly as possible, whilemaintaining CVP and wedge pressures at acceptable values. Rewarming thenbegan. During this period, HLB solution was periodically drained fromthe animal's circulation while adding new HLB solution to the perfusionapparatus.

[0075] The animal was warmed keeping the CVP below 5 mm Hg. When theesophageal temperature reached 15° C., the animal's own whole bloodcollected during cooling was added to the circuit, replacing the HLBsolution. Following this, enough donor whole blood was added to raisethe hematocrit above 20%.

[0076] Heartbeat resumed when the body temperature rose. As thetemperature rose, the hematocrit was elevated until it reached normalbetween 25-35%. As the temperature climbed above 25° C. Lasix wasinjected iv. Over the next hour, the baboon was warmed. Ventilation wasinitiated, and the baboon's body temperature rose to 37° C. A dopaminei.v. drip was begun when body temperature reached 25° C. As the baboonwas warmed further, the dopamine drip was increased, and then, as bloodpressure climbed, it was reduced, and then discontinued. The animal wasremoved from bypass, the catheters and cannulas pulled, and incisionsclosed. Sodium bicarbonate was administered iv. as needed to manageacidosis. After revival, the animal was weaned from the ventilator.

[0077] The circulating fluid was sampled periodically from the rightfemoral artery and the pH, electrolyte levels and hematocrit weredetermined and are reported in Table I.

[0078] Solution Compositions (in mM Concentrations Except HES [g/l])Solution HES NaCL MgCl CaCl₂ Glucose NaLactate HL 60 115 0.25 2.5 5 28

[0079] HLB has the same composition as HL but includes in addition 5 mMNaHCO₃. HES is high molecular weight hydroxyethyl starch. TABLE I SampleElapse time pH Ca++ K+ HCT* 1 0:00 7.654 9.3 3.1 40 2 0:15 7.646 3 0:317.555 4 0:58 7.536 8.9 2.7 39 5 1:13 7.627 8.9 3.2 25 6 1:40 7.340 <<0.5 7 1:47 7.201 < 0.5 8 1:56 7.455 2.4 0.25 9 2:09 7.326 0.25 10 3:017.468 10.4 3.2 11 3:53 7.498 10.5 2.9 12 4:11 7.657 9.5 3.9 5.0 13 4:187.439 6.7 5.9 22 14 4:35 7.593 8.9 4.3 13 15 5:02 7.380 8.0 3.2 23 165:23 7.285 8.8 2.7 26 17 5:41 7.110 9.2 3.1 32 18 6:07 9.0 4.4 36 196:11 7.038 7.8 3.8 34 20 6:32 7.284 3.3 32 21 6:57 7.437

EXAMPLE II Reviving a Hamster After Ice-Cold Blood Substitution

[0080] In this experiment an 80 g female hamster was revived afterchilling below 4° C. The animal was anesthetized by i.m. injection ofketarnine and surrounded in crushed ice. When its body temperaturereached 12°-16° C., it was removed from the ice and placed on a surgicalstage. Its right femoral vein was cannulated with a modified 24 gaugeangiocath, and its right femoral artery was cannulated with amicrocannula.

[0081] The micro-cannula was attached to a line which was also connectedto a reservoir and a pump, and the reservoir was chilled in crushed iceand contained ice-cold hypothermic blood substitute solution describedin example I as HL. The animal was ventilated with 100% O₂ and perfusedwith 7 ml of blood substitute solution (150% of its estimated bloodvolume), until its hematocrit fell to 6%, its heart was stopped with ani.v. injection of 0.15 ml of 1M KCl During the perfusion, the bloodsubstitute, whose initial pH was 5.5, comprised much of the venouseffluent. The pH of the venous effluent first fell from 7.35 to 7.23,and then rose to 7.41, and later 7.55.

[0082] After 35 minutes of perfusion with ice-cold blood substitutionperfusion was stopped and the animal maintained at the ice-point. After30 minutes, whole blood was infused into the femoral artery, and bloodsubstitute removed as a venous effluent.

[0083] The animal's heartbeat recovered after 25 minutes of bloodsubstitution and the hematocrit reached 48% within another 10 minutes,and perfusion was halted. Five minutes later, breathing began. Within 20minutes the animal was awake, and within one hour, it regained normalposture and was able to move about its cage. This recovery was thequickest ever observed using ice-cold blood substitution. The animalsurvived without complications for at least one week after theexperiment and appeared normal.

[0084] The experiment confirmed the utility of the present formulationfor use in ice-cold blood substitution. The solution containing sodiumlactate initially has a pH of between 4 and 6, but after the lactate ismetabolized, the resulting venous effluent has an alkaline pH, which cancounteract acidity which may develop during rewarming. Also, there issome evidence accumulating that hypothermia can cause leakage of bloodproteins out of the circulation, and into tissue, creating edema. Thenew formulation contains high molecular weight hydroxyethyl starch whichhas an average molecular weight of 480,000, and is therefore less likelyto leak out of the vasculature than albumin, found in blood, or dextran40.

EXAMPLE III HL Solution as an Artificial Plasma

[0085] A 80 g female hamster was injected im with an anesthetic mixtureof ketamine, xylazine and acepromazine, and its right femoral vein andartery were cannulated as described in Example II. The animal wasperfused with the artificial plasma solution. designated HL in Example Icontaining however 2 mM K+, until its femoral venous blood had ahematocrit of 18%. An equal amount of venous effluent was removed as theartificial plasma solution was infused into the femoral artery.

[0086] The catheters were removed and the incisions closed. The animalrecovered from the anesthesia and survives at this writing, one weekafter the experiment. Since the initial hematocrit was 48%, dilution ofthe blood to 18/48 of its initial concentration represents a bloodsubstitution of 62.5%.

EXAMPLE IV Effect of Perfusate Composition on pH

[0087] Hamsters were injected i.m. with an anesthetic ketamine. Afterthey were anethesized they were placed in crushed ice. When bodytemperature cooled to about 12.degree. C. as measured by a rectalthermocouple, the hamsters were placed on a surgical stage. The carotidartery and jugular vein were exposed and cannulas were inserted intoeach. Body temperature was lowered further to below 5 degrees centigradeand using a peristaltic pump perfusate was pumped into the artery atabout 0.3 ml per minute while venous effluent was collected and the pHof the effluent solution measured.

[0088] The perfusate solution consisted of the following constituents:High molecular weight hydroxyethyl starch 0.06 grams/ml Sodium chloride115 mM Magnesium chloride 0.25 mM Calcium chloride 2.5 mM Glucose 5 mM

[0089] A) Using the perfusate indicated above including 28 mM sodiumlactate, having an initial pH 6.0 at room temperature (r.t.), thefollowing pHs were obtained for samples of the effluent solutions:volume (ml) out pH 1 7.3 2 7.2 5 7.0 20 6.9

[0090] Effluent samples were combined and the pH measured. The pH of thecombined samples was 7.0.

[0091] B) Using the perfusate indicated above including Tris buffer (25mM, having an initial pH 7.8 r.t., the following pHs were obtained forsamples of the effluent solutions: volume (ml) out pH 1 7.3 2 7.25 47.28 8 7.3 11 7.16 20 7.2

[0092] Effluent samples were combined and the pH measured. The pH of thecombined samples was 7.2.

[0093] C) Using the perfusate indicated above including 28 mM sodiumlactate and 10 mM sodium bicarbonate, having an initial pH 8.3 r.t., thefollowing pHs were obtained for samples of the effluent solutions:volume (ml) out pH 1 7.3 2 7.2 5 7.32 8 7.41 12 7.53 20 7.55

[0094] Effluent samples were combined and the pH measured. The pH of thecombined samples was 7.5.

[0095] D) Using the perfusate indicated above including 28 mM sodiumlactate and 5 mM sodium bicarbonate, having an initial pH 8.2 r.t., thefollowing pHs were obtained for samples of the effluent solutions:volume (ml) out pH 1 7.3 3 7.28 6 7.35 8 7.33 10 7.38 12 7.50 15 7.53 207.51

[0096] Effluent samples were combined and the pH measured. The pH of thecombined samples was 7.5.

[0097] E) Using 2 solution system in which the solutions had thefollowing compositions:

[0098] 1) the perfusate indicated above including 28 mM sodium lactatehaving an initial pH 6.0 r.t.; and 2) the perfusate indicated aboveincluding 28 mM sodium lactate and 5 mM sodium bicarbonate, having aninitial pH 8.2 r.t.

[0099] The following pHs were obtained for the samples of the effluentsolutions: volume out pH With 1: 1 7.25 4 7.13 8 7.11 Switch to 2: 107.41 14 7.44 17 7.45 20 7.49 23 7.4

[0100] Effluent samples of ml 10-23 were combined and the pH measured.The pH of the combined sample was 7.41.

[0101] This series of experiments show that the addition of only 5 mMsodium bicarbonate to the lactate-buffered perfusate solution issufficient to maintain near normal pH during total body washout atice-cold temperatures. Interestingly and unexpectedly thelactate/bicarbonate buffer system is superior to biological buffers suchas Tris when flushing animals with large volumes of solution at coldtemperatures. Using the biologic buffers pH generally falls well belownormal. Using only lactate the pH falls to an even lower pH (however useof lactate only when perfusing warm metabolically active animals,results in normal to basic pH). Using lactate with the addition of asmall amount of bicarbonate, provided venous effluent with a near normalpH It was particularly surprising that such a small amount ofbicarbonate added to the solution could maintain adequate pH of venouseffluent when perfusing large volumes.

[0102] It will be apparent from the foregoing that the blood plasmasubstitute solutions described herein may also be used to increase thecirculating fluid volume of a hypovolemic subject. If used for thispurpose, as described above, the concentration of the water solubleoncotic agent wherein the blood plasma substitute solution comprises asingle oncotic agent will have the same concentration ranges as theplasma expander solutions. Thus for example when Dextran 40 or lowmolecular weight hydroxyethyl starch is used in the solution accordingto the invention its concentration is in a range of 6.0 to 8.5%. Asolution comprising about 8% Dextran 40 (wt/wt) or about 80 grams (g)per liter (l) of water is generally used. When Dextran 70 or highmolecular weight hydroxyethyl starch is used in the solution accordingto the invention its concentration is in a range of 5.5% to 6.5%. Asolution comprising about 6% high molecular weight hydroxyethyl starch(wt/wt) or about 60 grams (g) per liter (l) of water is generally used.

[0103] The new solutions according to the invention will be readily seento confer several advantages over existing blood substitute solutions.Since the new formulation contains no biological buffer, nounphysiological components are present. All of the ingredients in theformula occur naturally in living mammals in significant quantities.Furthermore, the low pH of this formulation allows it to be terminallysterilized more readily. The components, being naturally occurringcompounds omnipresent in significant quantities are inexpensive, and cantherefore be produced at less cost. Since the formulation has a slightlyacid pH, it has storage advantages as well.

What is claims is:
 1. A method for increasing the circulating volume ofa hypovolemic subject comprising administering to said subject aplasma-like substance comprising an aqueous solution of at least onewater soluble polysaccharide oncotic agent and a small organic acidsalt, with the proviso that: (a) when said oncotic agent is ahydroxyethyl starch, said hydroxyethyl starch is selected from the groupconsisting of high molecular weight and low molecular weighthydroxyethyl starches; and (b) said solution has at least one of thefollowing characteristics: (i) is terminally heat sterilized; (ii) doesnot contain a biological buffer; and (iii) has a pH between 4 and 6.5.2. The method according to claim 1, wherein said polysaccharide oncoticagent is a glucan polymer.
 3. The method according to claim 2, whereinsaid glucan polymer is a hydroxyethyl starch.
 4. The method according toclaim 3, wherein said hydroxyethyl starch has a molar substitution of0.7.
 5. The method according to claim 3, wherein said hydroxyethylstarch has a molar substitution of 0.45.
 6. The method according toclaim 1, wherein said small organic acid salt is a salt of a smallorganic acid ion that may be metabolized.
 7. The method according toclaim 6, wherein said small organic acid ion is selected from the groupconsisting lactate, acetate, pyruvate, gluconate and succinate.
 8. Themethod according to claim 1, wherein said solution does not comprise abiological buffer.
 9. The method according to claim 1, wherein saidsolution is a terminally heat sterilized solution.
 10. The methodaccording to claim 1, wherein said solution has a pH between 4 and 6.5.11. A method for increasing the circulating volume of a hypovolemicsubject comprising administering to said subject a plasma-like substancecomprising an aqueous solution of at least one water solublehydroxyethyl starch selected from the group consisting of high and lowmolecular weight hydroxyethyl starches and a small organic acid salt ofan ion selected from the group consisting of lactate, acetate, pyruvate,gluconate and succinate, wherein said solution has a pH between 4 and6.5.
 12. The method according to claim 11, wherein said hydroxyethylstarch has a molar substitution of 0.7.
 13. The method according toclaim 12, wherein said hydroxyethyl starch is hetastarch.
 14. The methodaccording to claim 11, wherein said hydroxyethyl starch has a molarsubstitution of 0.45.
 15. The method according to claim 14, wherein saidhydroxyethyl starch is pentastarch.
 16. The method according to claim11, wherein said solution does not comprise a biological buffer.
 17. Themethod according to claim 11, wherein said solution is a terminally heatsterilized solution.
 18. A plasma-like substance comprising an aqueoussolution of at least one water soluble polysaccharide oncotic agent anda small organic acid salt, with the proviso that: (a) when said oncoticagent is a hydroxyethyl starch, said hydroxyethyl starch is selectedfrom the group consisting of high molecular weight and low molecularweight hydroxyethyl starches; and (b) said solution has at least one ofthe following characteristics: (i) is terminally heat sterilized; (ii)does not contain a biological buffer; and (iii) has a pH between 4 and6.5.
 19. The plasma-like substance according to claim 18, wherein saidpolysaccharide oncotic agent is a glucan polymer.
 20. The plasma-likesubstance according to claim 19, wherein said glucan polymer is ahydroxyethyl starch.
 21. The plasma-like substance according to claim20, wherein said hydroxyethyl starch has a molar substitution of 0.7.22. The plasma-like substance according to claim 20, wherein saidhydroxyethyl starch has a molar substitution of 0.45.
 23. Theplasma-like substance according to claim 18, wherein said small organicacid salt is a salt of a small organic acid ion that may be metabolized.24. The plasma-like substance according to claim 23, wherein said smallorganic acid ion is selected from the group consisting lactate, acetate,pyruvate, gluconate and succinate.
 25. The plasma-like substanceaccording to claim 18, wherein said solution does not comprise abiological buffer.
 26. The plasma-like substance according to claim 18,wherein said solution is a terminally heat sterilized solution.
 27. Theplasma-like substance according to claim 18, wherein said solution has apH between 4 and 6.5.
 28. A plasma-like substance comprising an aqueoussolution of at least one water soluble hydroxyethyl starch selected fromthe group consisting of high and low molecular weight hydroxyethylstarches and a small organic acid salt of an ion selected from the groupconsisting of lactate, acetate, pyruvate, gluconate and succinate,wherein said solution has a pH between 4 and 6.5.
 29. The plasma-likesubstance according to claim 28, wherein said hydroxyethyl starch has amolar substitution of 0.7.
 30. The plasma-like substance according toclaim 29, wherein said hydroxyethyl starch is hetastarch.
 31. Theplasma-like according to claim 28, wherein said hydroxyethyl starch hasa molar substitution of 0.45.
 32. The plasma-like according to claim 31,wherein said hydroxyethyl starch is pentastarch.
 33. The plasma-likeaccording to claim 28, wherein said solution does not comprise abiological buffer.
 34. The plasma-like according to claim 28, whereinsaid solution is a terminally heat sterilized solution.